Method of manufacturing pyridinecarboxylic acids



Patented Mar. 12, 1946 i METHOD OF MANUFACTURING PYRIDINE- CARBOXYLIC ACIDS Francis E. .Cislak and William R. Wheeler, In-

dianapolis, Ind., assignors to Reilly Tar & Chemical Corporation, Indianapolis, Ind., corporation of Indiana No Drawing. Application March 25, 1942, Serial No. 436,171

Claims.

Our invention relates to a process of manufacturing pyridinecarboxylic acids by the oxidation of phosphates of alkyl pyridines, quinoline, isoquinoline, and alkyl quinolines, which bases are oxygen-free pyridine-ring-containing compounds, which contain no nitrogen outside the pyridine ring.

Heretofore pyridinecarboxylic acids have been prepared by the oxidation of alkyl pyridines, quinoline, isoquinoline, or alkyl quinolines with potassium permanganate. The preparation of pyridinecarboxylic acids in this manner is costly and troublesome; moreover, the potassium permanganate is not only an expensive oxidizing agent, but it is not now available except for essential war uses.

We have invented a process of producing pyridinecarboxylic acids from phosphates of alkyl pyridines, quinoline, isoquinoline, and alkyl quinolines which utilizes nitric acid as the oxidizing agent. Nitric acid is a readily available and inexpensive oxidizing agent which can easily be separated from the desired oxidation products; furthermore, the resulting nitric oxides can be reconverted into nitric acid merely by absorption in aerated water. Heretofore there has been no known method of utilizing nitric acid for the oxidation of the above-mentioned pyridine-ringcontaining compounds. I v

Fundamentally, our process consists in oxidizing the phosphates of the said pyridine-ringcontaining compounds with nitric acid at elevated temperatures, with or without oxidation catalysts; if desired, with subsequent elimination of phosphoric acid.

The preferred manner in which our invention may be practiced is described more specifically, and the variation permitted in detail is illustrated, in'the following examples.

Example 1.In a one-liter flask, form a solution of 47 grams of 96% 3-picoline, 125 grams of concentrated phosphoric acid (85%), and 25 cc. of concentrated nitric acid (70%). Reflux this solution for about 2-3 hours; and then distill off the water formed by the oxidation (as well as the water initially added with th nitric acid), and with it any remaining nitric acid. It is desirable to stop the distillation when the temperature of the liquid remaining in the flask reaches about 200 C.

Now cool the contents of the flask to about 120 C., and repeat the nitric-acid oxidation. To this end, add about 25 co. more concentrated nitric acid. Reflux the solution for about 2-3 (0'1. zoo-295.5)

hours. Distill oil the water, and the remaining nitric acid.

Repeat the procedure of the immediately preceding paragraph until atotal of about 275 cc. of the concentrated nitric acid has been put through. When the last distillation has been completed, remove any remaining traces of nitric acid from the residue in the flask by aerating the hot solution.

' Then cool the said residue and dilute it to about 300 cc. with water.

If it is desired to eliminate phosphoric acid, add about 45 grams of sodium hydroxide to the resulting aqueous solution, to form a sodiumphosphate bufiered solution; whereupon 3-pyridine-carboxylic acid (which is nicotinic acid) crystallizes out. This may be separated and purified in known manner.

Example 2.-In place of intermittently adding small portions of nitric acid to the 3-picoline phosphate, refluxing, and distilling, as in Example 1, we can continuously pass vaporiz d nitric acid through the hot 3-picoline phosphate and continuously distill off the water and excess nitric acid. The entering nitric-acid vapor may be mixed with oxygen or air; in which case the amount of nitric acid required is diminished.

In a one-liter flask form a solution of 47 grams of 93% 3-picoline and 125 grams of 85% phosphoric acid. Heat this solution to a temperature of about 150-250 0., preferably about 170 C., and maintain it at this temperature. Slowly (over a period of 15 to 25 hours) vaporize 300 cc. of 70% nitric acid and pass it into the picolinephosphate solution; condense the water, the unreacted nitric acid, and the nitric oxides evolved. After all the vaporized nitric acid has been passed into the picoline-phosphate solution, aerate the hot solution to remove residual traces of nitric acid.

Cool and dilute the picoline-phosphate solution, and if desired separate the nicotinic acid, as in Example 1.

Example 3.In place of the 3-picolin of Examples 1 and 2, we can use any of the other alkyl pyridines, such as 2-picoline, 4-picoline, 2,6

lutidine, 2-ethy1 pyridine, etc., to obtain corresponding pyridinecarboxylic acids.

Example 4.In place of the 3-picoline of Examples l and 2, we can use quinoline or isoquinoline, to obtain pyridinedicarboxylic'acids, or we can use alkyl quinolines to obtain pyridinedicarboxylic acids or alkyl pyridinedicarboxylic acids.

For instance, a solution of 64.5 g. of quinoline and 140 g. of phosphoric acid is placed in clinic acid in known manner.

any suitable vessel for bringing about intimate contact of gas and liquid, and heated to 150430 0., preferably about 180 0.; and the vapor of 500 to 800 cc. of nitric acid (70%) is passed through over a period'of 24-48 hours. The reaction mixture is cooled, and diluted with water; whereupon any by-products which precipitate are filtered off. The filtrate is made alkaline with potassium hydroxide, 'and evaporated to dryness. The dry residue contains both potassium phos phate and potassium quinolinate. The latter may be suitably separated from the former, as by extraction with alcohol, and convertediinto quin- We claim as our invention:

1. The method of producing a pyridinecarboxylic acid, which comprises oxidizing a phosphate of a pyridine-ring-containing compound of the class consisting of alkyl pyridines, quinoline, isoquinoline, and alkyl quinolines, with nitric acid at an elevated temperature sufllciently high to vaporize nitric acid.

2. The method of producing a D dinecarboxylic acid as described in claim 1, in which the pyridine-ring-containing compound is 3-pic0line.

3. The method of producing a pyridinecarboxylic acid as described in claim 1, in which the pyridine-ring-containing compound is quinoline.

4. The method of producing a pyridinecarboxylic acid as described in claim 1, in which the pyridine-ring-containing compound is z-picoline.

5. The method of producing a pyridinecarboxylic acid as described in claim 1, with the addition or the step of eliminating phosphoric acid.

6. The method of producing a pyridinecarboxylic acid, which comprises treating a pyridinering-containing compound of the class consisting of alkyl pyridines, quinoline, isoquinoline, and alkyl quinolines, with phosphoric acid and nitric acid at an elevated temperature sufliciently high to vaporize nitric acid.

7. The method of producing a pyridinecarboxylic acid as described in claim 6, in which the pyridine-ring-containing compound is 3-picoline.

8. The method of producing a pyridinecarboxylic acid as described in claim 6, in which the pyridine-ring-containing compound is quinoline.

9. The method of producing a pyridinecarboxylic acid as described in claim 6, in which the pyridine-ring-containing compound is 2-picoline.

10. The method of producing a pyridinecarboxylic acid as described in claim 6, with the addition of the step of eliminating phosphoric acid.

. FRANCIS E, CISLAK.

WILLIAM R. WHEELER. 

